Which of the following is necessary to increase the rate of a reaction? a. a decrease in the frequency of collisions b. an increase in the frequency of collisions c. a decrease in the frequency of successful collisions d. an increase in the frequency of successful collisions

Rate of the reaction is the decrease in concentration of the reactant or increase in the concentration of products per unit time.

Factors like concentration (pressure) of the reactant, nature of reactant, catalyst, surface area of the reactant, affect the reaction rate. Greater the concentration of the reactant, higher will be the number of effective collisions between the reactant molecules per unit time. So, the rate of reaction would increase with increase in frequency of successful collisions due to the increase in concentration of the reactants.

So, the correct answer is D. an increase in the frequency of successful collisions